Carbon Monoliths in Catalysis

KAREN M. DE LATHOUDER, EDWIN CREZEE, FREER KAPTEUN, and JACOB A. MOULUN 

Recently, there has been a growing interest in the use of monohthic structures for (bio)chemical conversion and adsorption processes. A very versatile type of monolith is based on carbon. The combined properties of carbon and monolithic structures create a support with great potential. In this chapter we describe recent developments in the field of carbon-based monolithic structures with respect to preparation, support properties, and application in catalytic processes. Furthermore, two examples are used to demonstrate the approach and possible pitfalls when using carbon (coated) monoliths in catalysis. 

Carbon Materials for Catalysis, Edited by Philippe Serp and Josd Luts Figueiredo Copyright 2009 John Wiley Sons, Inc. 

Cell Density Geometric Surface Area (m /m ) Void Fraction Channel Diameter (mm) Wall Thickness (irm) 

Carbon-based monoliths can be of the integral or coated type [5,6]. For practical applications, several requirements are set to monolithic structures. For a coated type of monolithic support, the mechanical properties are adopted from the ceramic or metallic monoliths. It is, however, important that the coating adhere well to the monolith to prevent flaking and subsequent loss of active 

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FIGURE 32 Initial rates of reaction in catalysis by free lipase and immobilized lipase (Novozyme, and catalyst supported on 200 cpsi carbon monolith) in the acylation of butanol with vinyl acetate in an organic medium at 300 K. 

Table 11.2 Applications of Carbon-Based Monoliths in Catalysis...

In the review by Armor [1] a variety of pollutants are discussed with a focus on commercially applied processes using catalysis as a solution. Issues such as the removal of NO.v, SO.v, chlorofluorohydrocarbons (CFC), VOC, carbon monoxide, auto exhaust emission, ozone, nitrous oxide, byproducts from chemicals production, odor control, and toxic gas removal are discussed. In another review Armor [2] discusses specific topics such as monolith technology, new catalytic materials, and specific processes. Additionally, key suggestions for future research effort are given. 

Lozano, P., Garcia-Verdugo, E., Piamtongkam, R., Karbass, N., De Diego, T., Burguete, M.I., Luis, S.V., and Iborra, J.L. (2007) Bioreactors based on monolith-supported ionic liquid phase for enzyme catalysis in supercritical carbon dioxide. Adv. Synth. Catal., 349 (7), 1077-1084. 

An important feature of these materials is that metal-doped monolithic carbon gels can readily be prepared (see below). These are emergent materials in the field of heterogeneous catalysis, and their use will grow in the near future, due... 

Areas in which further developments are expected are related to the optimization of the solution of air and water pollution, gas purification (removal of oxides of sulfur and nitrogen, of hydrogen sulfide, motor vehicle emissions, etc.), gas separation, mineral industries, regeneration, etc. Many of these areas will require the use of new forms of activated carbon such as cloth, felts, fibers, monoliths, etc., and consequently a search for the appropriate precursor and preparation mode is essential. Other areas in continuous progress will be gas storage, carbon molecular sieves and heterogeneous catalysis, all of them requiring considerable research efforts in the next few years. 

Despite the high mechanical and thermal stability of these stmctures, which are by far sufSdent for short- and medium-term analytical applications as wdl as applications in heterogeneous catalysis, " tert-allylic carbons located at the surface of a monolithic stmcture tend to be oxidized, resulting in a slow change of surface polarity of such monolithic columns. Consequently, the typical long-term stability of NBE-based, ROMP-derived columns is limited to less than 1000 injections. To solve this problem, a novel monomer/ cross-linker system had to be introduced. For these purposes, Buchmeiser et al. devdoped a polymerization system based on... 

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